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There are many examples of displays mounted on the head, sunglasses, eyeglasses and the like (for example Perera, U.S. Pat. No. 4,867,551). Perera describes a display mounted on eyeglasses, the limitation of which is the high degree of occlusion of the user""s field of view beyond the display, and the use of non-axial optics that introduces distortion. Other companies, such as VirtualVision, provide displays that are suspended by a cable, gooseneck fixture or other mechanical support in front of one or both of the user""s eyes. Similarly, students at the MIT Media Laboratory have been mounting displays from Reflection Technology on eyewear, in order to provide a computer display in a mobile fashion. These approaches also highly limit the user""s view of the surroundings.
Generally, head-mounted and helmet-mounted display systems are based on miniature displays having a diagonal dimension of 4 cm or less. The display systems that use such miniature displays must provide a lens near the eye for magnification, and to make possible comfortable viewing at near distances. We term the lens and any other associated optics that must be placed near the eye the xe2x80x9ceyepiece.xe2x80x9d Most prior art head-mounted systems also place the display (for example a miniature liquid crystal flat panel display) near the eye as well, which requires both a support fixture for the eyepiece, and a conduit for electrical cables to the display. These components (wires, liquid crystal display, illumination source and any other required circuits) are placed within an opaque housing near the eye. Consequently, such systems block a portion of the user""s visual field, and also obscure the user""s face. For liquid crystal displays, the illumination source accounts for a large amount of the volume of the eyepiece.
In a recent patent (U.S. Pat. No. 6,023,372), we described a method of supporting an eyepiece near the eye at the end of a transparent opto-mechanical structure (FIG. 1). Data or images are relayed to the device by a cable which may comprise wire, one or more optical fibers as described in U.S. Pat. No. 5,715,337, or a fiber optic coherent bundle image conduit. The advantage of this prior art approach is the low obscuration of the user""s vision inherent in the use of a transparent opto-mechanical support for the eyepiece.
This invention comprises a new approach to a light weight, compact head-mounted display system that combines an image relay system and mechanical support with a simple mounting system that can be applied to eyeglasses or other head gear. The invention involves mounting of a display, such as a liquid crystal display, against an eyepiece at the end of a clear supporting structure, with illumination provided through a transparent opto-mechanical support fixture that suspends the eyepiece near the eye. The opto-mechanical support fixture may be like that described in U.S. Pat. No. 6,023,372, the disclosure of which is incorporated by reference herein. In an alternative embodiment, the invention involves mounting of the liquid crystal display against an eyepiece with a visually minimal opaque mechanical support, and with the illumination provided through free space. The device is particularly suitable for use as an interface to computers, personal digital assistants, and cellular telephones.
More particularly, the invention provides a compact, head-mountable display device for transmitting an image to a user""s eye. The display device includes a support comprising an elongated member configured to allow passage of ambient light across a direction of elongation of the elongated member to a user""s eye. A display, such as an LCD, is supported by the support and is operative to provide an image. An eyepiece assembly is supported by the support fixture in proximity to the display to receive the image from the display and to direct the image to the user""s eye. The support also defines an illumination path along the elongated member, and the display is located to receive illumination light on the illumination path from a light source.
The invention is advantageous in that it permits the display to be located near the eyepiece, so that the eyepiece may have a shorter focal length and consequently provide higher magnification, and it allows the illumination source to be remote from the eyepiece and display. As can be seen in the drawings, the display itself is relatively low in volume, and in the case of an LCD is largely glass, and thus can be integrated in the eyepiece without a high degree of obscuration of the user""s vision. Although the eyepiece has slightly greater obscuration than the prior art device in U.S. Pat. No. 6,023,372, the greater magnification obtainable from the shorter focal length of the eyepiece is an advantage that may be preferable in many applications.